On men's shirts what the purpose of the yoke? (1 Viewer)

[Jeremy Illingworth]

Why is it there? Dress shirts seem to always have them but more casual button up shirts don't. The yoke is always two layers of fabric thick making it appear that its there for more than just apperance; otherwise why not single layer? Is there a historical purpose for it (I can't think of a modern one) is it just for looks?
jeremy

 

[Eric Scott]

The main purpose is reinforcement at the major stress points, in order to keep the garment in proper form.